Conventionally, the aircraft starter generator is driven by a high-pressure rotating shaft of the two-shaft jet engine. Disadvantageously, this fails to accommodate an increase of electric power to be supplied to a huge number of electronic devices newly installed in the aircraft, which results in a higher risk for engine stall at lower output operations of the engine such as ground idling or descending flight. In addition, a future higher bypass ratio of the engine will increase that risk which may not be eliminated by the conventional constant frequency (CF) or variable frequency (VF) integrated drive generator (IDG) which incorporates a continuously variable transmission allowing to generate electric power with a constant frequency irrespective of the rotation number of the engine. To cope with this, there has been proposed a constant frequency (CF) integrated drive generator (IDG) using a traction drive continuously variable transmission, which is expected to meet the requirements for introduction of electronic components into the aircraft (see Japanese Patent Application No. 2009-026220.)
Another key technology is the electric starter which may be replaced by the conventional air compressor starter. The electric starter, because it can be used as a power generator after the engine is started, will contribute to its weight and cost saving. However, since the compressor is driven by the high-pressure shaft, the starter generator is required to be connected to the high-pressure shaft in order to start the engine, which may result in the engine stall. Also, the electric power generated by the generator has a variable frequency.
In addition, JP (A) 2008-38902, the U.S. Pat. Nos. 3,274,855, 3,786,696, 4,315,442, and UK Patent No. 1199145 disclose to modify the conventional IDG to work as a starter generator drivingly connected to the high-pressure rotating shaft, rather than the low-pressure rotating shaft.
Further, in order to use more electronic components in the aircraft in place of mechanical components, it has been proposed to use a starter generator driven by the high-pressure rotating shaft and an integrated drive generator driven by the low-pressure rotating shaft. This requires two different systems, i.e., variable frequency and constant frequency systems, which results in a complexity of the power system of the aircraft, an increase the number of spare parts, and an increase of its production cost.
Another technique may be employed to modify the integrated drive generator and connect it to the high-pressure rotating shaft. However, this requires the traction drive to transmit a large torque at the start of the engine, which may cause unwanted heat-fusing and/or metallic fatigue in the contact surfaces of the traction drive.
Accordingly, the present invention is to provide an aircraft starter generator in which an electric power with constant frequency is generated and a starter operation is carried out by the use of the high-pressure rotating shaft, which simplifies the structure of the apparatus and attains a cost reduction of the starter generator.